Thermal and spectroscopic studies of terbium(III) and dysprosium(III) complexes with piperidin-4-ones

Article abstract of DOI:10.1016/S0040-6031(02)00563-4

Terbium(III) and dysprosium(III) nitrate complexes with variously substituted 2,6-diphenylpiperidin-4-ones (L¹)-(L¹⁰) of general formula [Ln(L)(NO₃)₂(H₂O)₂]NO₃ have been synthesized. These complexes have been characterized by analytical, spectral and thermal studies. Molar conductance data show that these complexes are 1:1 electrolytes. The presence of two coordinated water molecules is confirmed by thermal and infrared spectral studies. IR spectral data indicate that piperidin-4-ones, in spite of having two coordinating sites, are monodentate, coordinating only through ring nitrogen. The IR and conductance data reveal the presence of two bidentate and one ionic nitrate groups. The nephelauxetic ratio (β), covalency factor (b^1/2) and Sinha's parameter (δ) evaluated from electronic spectral data of dysprosium(III) complexes indicate a little covalency in metal-ligand bonding.

Full text of DOI:10.1016/S0040-6031(02)00563-4

Thermochimica Acta 401 (2003) 187–197
Thermal and spectroscopic studies of terbium(III) and
dysprosium(III) complexes with piperidin-4-ones
Kuppusamy Selvaraja,∗, Chinniagounder Theivarasub
Department of Chemistry, PSG College of Arts and Science, Coimbatore, Tamilnadu 641014, India
a
b
Department of Chemistry, PSG College of Technology, Coimbatore, Tamilnadu 641004, India
Received 4 November 2002; accepted 18 November 2002
Abstract
Terbium(III) and dysprosium(III) nitrate complexes with variously substituted 2,6-diphenylpiperidin-4-ones (L1)–(L10) of
general formula [Ln(L)(NO3)2(H2O)2]NO3 have been synthesized. These complexes have been characterized by analytical,
spectral and thermal studies. Molar conductance data show that these complexes are 1:1 electrolytes. The presence of two coor-
dinated water molecules is confirmed by thermal and infrared spectral studies. IR spectral data indicate that piperidin-4-ones,
in spite of having two coordinating sites, are monodentate, coordinating only through ring nitrogen. The IR and conductance
data reveal the presence of two bidentate and one ionic nitrate groups. The nephelauxetic ratio (β), covalency factor (b1/2
)
and Sinha’s parameter (δ) evaluated from electronic spectral data of dysprosium(III) complexes indicate a little covalency in
metal–ligand bonding.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Piperidin-4-ones; Terbium(III) and dysprosium(III) complexes; Thermal decomposition
1. Introduction
[12]. Recently, we have reported the preparation and
characterization of samarium(III) [13], cobalt(II) [14]
and cerium(III) [15] complexes with piperidin-4-ones
in which it has been proved that only the ring nitro-
gen and not the carbonyl group of piperidin-4-ones
coordinates with metal ions. In continuation of our
earlier work, we now report the preparation, charac-
terization and thermal studies of terbium(III) and dys-
prosium(III) complexes containing piperidin-4-ones.
Lanthanide complexes containing a variety of het-
erocyclic compounds as ligands have been studied
extensively [1–5]. Although piperidin-4-ones have
been subjected to detailed kinetic and conforma-
tional studies [6–10], only a few reports are avail-
able [11–15] on the use of them as ligands in the
preparation of complexes. Cockburn et al., have used
N-benzylpiperidin-4-one as a ligand in the prepa-
ration of platinum and palladium complexes [11].
Venkappayya and co-workers have studied copper(II)
complexes of piperidin-4-ones and reported that
piperidin-4-ones act as bidentate ligands, coordinat-
ing through both the ring nitrogen and carbonyl group
2. Experimental
2.1. Chemicals
Terbium(III) and dysprosium(III) nitrates were pre-
pared by evaporating a solution of the corresponding
∗
Corresponding author.
0040-6031/03/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0040-6031(02)00563-4

Table 1
Physical and analytical data of the TbIII nitrate complexes
Complex
Number
Molecular weight
founda (calculated)
Yield
(%)
Decomposition
temperature (◦C)
Element found (calculated)
Conductance
(ꢀ−1 cm2 mol−1
)
Formula (empirical formula)
Tb%
C%
H%
N%
(Tb1)
(Tb2)
(Tb3)
(Tb4)
(Tb5)
(Tb6)
(Tb7)
(Tb8)
(Tb9)
[Tb(L1)(NO3)2(H2O)2]NO3 (C17H21N4O12Tb)
[Tb(L2)(NO3)2(H2O)2]NO3 (C18H23N4O12Tb)
[Tb(L3)(NO3)2(H2O)2]NO3 (C19H25N4O12Tb)
[Tb(L4)(NO3)2(H2O)2]NO3 (C20H27N4O12Tb)
[Tb(L5)(NO3)2(H2O)2]NO3 (C19H25N4O12Tb)
[Tb(L6)(NO3)2(H2O)2]NO3 (C18H23N4O12Tb)
[Tb(L7)(NO3)2(H2O)2]NO3 (C19H25N4O12Tb)
[Tb(L8)(NO3)2(H2O)2]NO3 (C20H27N4O12Tb)
[Tb(L9)(NO3)2(H2O)2]NO3 (C21H29N4O12Tb)
[Tb(L10)(NO3)2(H2O)2]NO3 (C20H27N4O12Tb)
630.95 (632.06)
647.00 (646.07)
662.52 (660.09)
676.00 (674.10)
662.25 (660.09)
648.37 (646.07)
658.59 (660.09)
676.16 (674.10)
689.26 (688.12)
676.23 (674.10)
70
85
80
75
90
70
75
70
70
70
325–326
155–156
160–162
139–141
168–169
>340
>340
>340
>340
>340
25.25 (25.14)
24.75 (24.60)
24.25 (24.08)
23.65 (23.58)
24.50 (24.08)
24.35 (24.60)
24.00 (24.08)
23.75 (23.58)
23.00 (23.10)
23.25 (23.58)
32.00 (32.27)
33.57 (33.43)
34.50 (34.54)
35.76 (35.60)
34.75 (34.54)
33.50 (33.43)
34.25 (34.54)
35.00 (35.60)
36.50 (36.62)
35.75 (35.60)
3.30 (3.35)
5.76 (3.59)
3.00 (3.21)
4.00 (4.04)
3.45 (3.21)
3.50 (3.59)
3.40 (3.21)
4.25 (4.04)
4.50 (4.25)
4.15 (4.04)
8.50 (8.86)
8.25 (8.67)
8.75 (8.48)
8.20 (8.31)
8.65 (8.48)
8.50 (8.67)
8.70 (8.48)
8.65 (8.31)
8.00 (8.14)
8.40 (8.31)
60
73
63
75
70
60
72
64
70
65
(Tb10
)
a Observed molecular weight × van’t Hoff factor.

Table 2
Physical and analytical data of the DyIII nitrate complexes
Complex
Number
Molecular weight
founda (calculated)
Yield
(%)
Decomposition
temperature (◦C)
Element found (calculated)
Conductance
(ꢀ−1 cm2 mol−1
)
Formula (empirical formula)
Dy%
C%
H%
N%
(Dy1)
(Dy2)
(Dy3)
(Dy4)
(Dy5)
(Dy6)
(Dy7)
(Dy8)
(Dy9)
[Dy(L1)(NO3)2(H2O)2]NO3 (C17H21N4O12Dy)
[Dy(L2)(NO3)2(H2O)2]NO3 (C18H23N4O12Dy)
[Dy(L3)(NO3)2(H2O)2]NO3 (C19H25N4O12Dy)
[Dy(L4)(NO3)2(H2O)2]NO3 (C20H27N4O12Dy)
[Dy(L5)(NO3)2(H2O)2]NO3 (C19H25N4O12Dy)
[Dy(L6)(NO3)2(H2O)2]NO3 (C18H23N4O12Dy)
[Dy(L7)(NO3)2(H2O)2]NO3 (C19H25N4O12Dy)
[Dy(L8)(NO3)2(H2O)2]NO3 (C20H27N4O12Dy)
[Dy(L9)(NO3)2(H2O)2]NO3 (C21H29N4O12Dy)
[Dy(L10)(NO3)2(H2O)2]NO3 (C20H27N4O12Dy)
636.50 (635.63)
652.75 (649.64)
665.00 (663.66)
676.27 (677.67)
664.71 (663.66)
648.72 (649.64)
665.81 (663.66)
678.00 (677.67)
693.15 (691.69)
670.96 (677.67)
65
75
70
70
75
60
65
65
60
65
132
148
>260
160–161
174–178
300
>270
>300
>300
140
25.00 (25.57)
25.25 (25.01)
24.72 (24.49)
24.00 (23.98)
24.75 (24.49)
25.25 (25.01)
24.85 (24.49)
23.75 (23.98)
23.00 (23.49)
23.56 (23.98)
32.50 (32.09)
33.85 (33.25)
34.05 (34.36)
35.56 (35.42)
34.55 (34.36)
33.45 (33.25)
34.36 (34.36)
35.75 (35.42)
36.50 (36.43)
35.25 (35.42)
3.55 (3.33)
3.75 (3.57)
3.95 (3.80)
4.00 (4.02)
3.75 (3.80)
3.65 (3.57)
3.42 (3.80)
4.25 (4.02)
4.55 (4.23)
4.15 (4.02)
8.50 (8.89)
8.45 (8.62)
8.65 (8.44)
8.57 (8.27)
8.50 (8.44)
8.37 (8.62)
8.20 (8.44)
8.35 (8.27)
8.00 (8.10)
8.72 (8.27)
65
60
53
48
50
55
62
47
56
52
(Dy10
)
a Observed molecular weight × van’t Hoff factor.

190
K. Selvaraj, C. Theivarasu / Thermochimica Acta 401 (2003) 187–197
Table 3
Important IR absorption bands (in cm−1) of the ligands and TbIII nitrate complexes
a
b
=
=
Complex ν(C O) ν(C O) ν(N–H) ν(O–H)
number
δ(HOH) ν4
ν1
ν2
ν6
ν3
ν5
ν4 − ν1 ν3 − ν5
(Tb1)
(Tb2)
(Tb3)
(Tb4)
(Tb5)
(Tb6)
(Tb7)
(Tb8)
(Tb9)
(Tb10
1700 s
1699 s
1701 s
1700 s
1701 s
1726 s
1722 s
1720 s
1710 s
1713 s
1720 s
1726 s
1730 s
1728 s
1732 s
1730 s
1727 s
1725 s
1718 s
1722 s
3400 s 3200–3600 b 1630 m 1470 s 1329 s 1040 m 822 w 745 s 698 s 141
3391 s 3200–3600 b 1638 m 1460 s 1310 s 1040 m 825 w 750 s 700 s 150
3389 s 3200–3600 b 1624 m 1470 s 1327 s 1040 m 825 w 754 s 698 s 143
3385 s 3200–3500 b 1627 m 1470 s 1320 s 1038 m 823 w 750 s 698 s 150
3398 s 3200–3600 b 1624 m 1458 s 1313 s 1028 m 825 w 750 s 698 s 145
3200–3600 b 1624 m 1480 s 1317 s 1038 m 823 w 750 s 698 s 163
3200–3600 b 1637 m 1475 s 1307 s 1040 m 825 w 750 s 698 s 168
3200–3600 b 1638 m 1485 s 1340 s 1038 m 825 w 750 s 698 s 145
3200–3600 b 1638 m 1480 s 1339 s 1041 m 825 w 750 s 700 s 141
3200–3600 b 1627 m 1480 s 1318 s 1040 m 823 w 750 s 698 s 162
47
50
56
52
52
52
52
52
50
52
)
Here, s: strong, b: broad, m: medium, w: weak.
a For ligands.
b For complexes.
oxide in concentrated HNO3. Purified ethanol (95%)
was used as a solvent.
tone and ether anddried under vacuum over P2O5. All
complexes are colourless amorphous solids, soluble
in methanol, dimethylforamide, dimethylsulfoxide
and acetonitrile and insoluble in acetone, ether, chlo-
roform and water. They are stable in air under dry
conditions.
2.2. Preparation of ligands and complexes
The various substituted 2,6-diphenylpiperidin-4-
ones (L1)–(L10) were prepared following reported
procedures [16,17]. The structures of the ligands
are reported in our earlier papers [13–15]. All the
complexes have been prepared by a general method.
A mixture of lanthanide(III) nitrate (5 mmol) and
piperidin-4-one (10 mmol) in ethanol (50 ml) was re-
fluxed on a water bath for 3–4 h. Subsequently, the
solvent was distilled off under reduced pressure. The
residue was repeatedly washed with hot ethanol, ace-
2.3. Physico-chemical techniques
The metal content of the complexes was determined
by complexometric ethylene diamine tetraacetic acid
(EDTA) titration [18] using xylenol orange as an
indicator at pH 6. Elemental analyses (C, H and N)
were determined using a Carlo Erba 1106 microan-
alytical instrument. Conductance measurements were
Table 4
Important IR absorption bands (in cm−1) of the ligands and DyIII nitrate complexes
a
b
=
=
Complex ν(C O) ν(C O) ν(N–H) ν(O–H)
number
δ(HOH) ν4
ν1
ν2
ν6
ν3
ν5
ν4 − ν1 ν3 − ν5
(Dy1)
(Dy2)
(Dy3)
(Dy4)
(Dy5)
(Dy6)
(Dy7)
(Dy8)
(Dy9)
(Dy10
1700 s
1699 s
1701 s
1700 s
1701 s
1726 s
1722 s
1720 s
1710 s
1713 s
1720 s
1726 s
1730 s
1728 s
1732 s
1730 s
1727 s
1725 s
1718 s
1722 s
3385 s 3200–3600 b 1638 m 1480 s 1319 s 1040 m 822 w 746 s 698 s 161
3389 s 3200–3600 b 1624 m 1470 s 1307 s 1040 m 823 w 750 s 698 s 163
3398 s 3200–3600 b 1624 m 1470 s 1319 s 1040 m 825 w 754 s 696 s 151
3371 s 3200–3600 b 1639 m 1470 s 1313 s 1038 m 825 w 750 s 698 s 157
3400 s 3200–3600 b 1637 m 1470 s 1288 s 1028 m 823 w 750 s 698 s 182
3200–3600 b 1624 m 1470 s 1316 s 1039 m 825 w 750 s 698 s 154
3200–3600 b 1638 m 1480 s 1329 s 1040 m 825 w 748 s 698 s 151
3200–3600 b 1627 m 1490 s 1330 s 1038 m 823 w 746 s 698 s 160
3200–3600 b 1624 m 1480 s 1329 s 1030 m 826 w 758 s 700 s 150
3200–3600 b 1624 m 1475 s 1325 s 1040 m 825 w 758 s 700 s 150
48
52
58
52
52
52
50
48
58
58
)
Here, s: strong, b: broad, m: medium, w: weak.
a For ligands.
b For complexes.

K. Selvaraj, C. Theivarasu / Thermochimica Acta 401 (2003) 187–197
191
performed on 10−3 mol l−1 solutions of the complexes
in acetonitrile using a type CM-82 Elico conductivity
bridge with a dip type conductivity cell fitted with a
platinum electrode (cell constant = 1.0 cm−1). The
molecular weight determinations have been carried out
by the depression of freezing point method using cam-
phor as the solvent in which the complexes are com-
pletely soluble. The experiments were repeated thrice
for each complex and the average values have been
taken. The results were found to agree with the calcu-
lated values within 2% error. The magnetic moments
of complexes were determined by the Gouy method at
room temperature. Electronic spectra of the complexes
were recorded on a Hitachi U-2000 spectrophotome-
ter. The IR spectra of the ligands and the complexes
were recorded on a Shimadzu FT-IR 8000 spectropho-
tometer in the 4000–400 cm−1 region using the KBr
disc technique. The simultaneous thermogravimetric
and differential thermal analyses (TG–DTA) were
carried out using a STA 1500 Shimadzu DT 40 ther-
mal analyzer. The thermal experiments were carried
out in air, using 3–5 mg samples at a heating rate of
10 ◦C min−1 in the temperature range from ambient
to 800 ◦C using a platinum cup as the sample holder.
Table 6
Bonding parameters obtained from electronic spectral data of the
dysprosium(III) complexes
Complex
β
b1/2
δ (%)
Number Formula
(Dy1)
(Dy2)
(Dy3)
(Dy4)
(Dy5)
(Dy6)
(Dy7)
(Dy8)
(Dy9)
(Dy10
[Dy(L1)(NO3)2(H2O)2]NO3 0.9965 0.0299 0.3512
[Dy(L2)(NO3)2(H2O)2]NO3 0.9972 0.0265 0.2808
[Dy(L3)(NO3)2(H2O)2]NO3 0.9945 0.0371 0.5530
[Dy(L4)(NO3)2(H2O)2]NO3 0.9956 0.0332 0.4419
[Dy(L5)(NO3)2(H2O)2]NO3 0.9968 0.0283 0.3210
[Dy(L6)(NO3)2(H2O)2]NO3 0.9925 0.0433 0.7557
[Dy(L7)(NO3)2(H2O)2]NO3 0.9950 0.0354 0.5025
[Dy(L8)(NO3)2(H2O)2]NO3 0.9963 0.0466 0.3714
[Dy(L9)(NO3)2(H2O)2]NO3 0.9978 0.0235 0.2205
[Dy(L10)(NO3)2(H2O)2]NO3 0.9939 0.0390 0.6137
)
ductance data, the stoichiometry of these complexes
can be represented as [Ln(L) (NO3)2(H2O)2]NO3
where, Ln: Tb and Dy, and L: piperidin-4-one.
3.1. Magnetic properties
The effective magnetic moments (µeff) of ter-
bium(III) and dysprosium(III) complexes are found
between 9.39–9.51 and 10.50–10.75 BM, respectively,
and do not deviate from Van Vleck values [20], re-
vealing the non-participation of 4f-electrons in bond
formation. It is also evident from the data that there
is no metal–metal interaction or spin–spin coupling.
3. Results and discussion
The analytical and conductance data of terbium(III)
and dysprosium(III) complexes are presented in
Tables 1 and 2, respectively. The molar conductance
data indicate that these complexes are 1:1 electrolytes
[19]. The observed molecular weights of terbium(III)
and dysprosium(III) complexes are found to be ex-
actly half of the expected value, showing that the van’t
Hoff factor is two. Based on the analytical and con-
3.2. Infrared spectra
The IR spectra of ligands and complexes were
mainly analysed for those specific frequencies which
are directly involved in the complex formation and
their values are recorded in Tables 3 and 4. The sharp
Table 5
Assignments of transitions in the electronic spectra of the dysprosium complexs (Dy2) and (Dy5)
Complexs
Number
(Dy2)
Absorption frequency (cm−1
)
Log ε (max)
Assignment
Formula
[Dy(L2)(NO3)2(H2O)2]NO3
23297
22150
21123
3.65
3.10
3.98
6H
→ 4G
11/2
→154/I2
15/2
→ 4F
9/2
(Dy5)
[Dy(L5)(NO3)2(H2O)2]NO3
23257
22165
21120
2.98
3.35
2.85
6H
→ 4G
11/2
→154/I2
15/2
→ 4F
9/2

192
K. Selvaraj, C. Theivarasu / Thermochimica Acta 401 (2003) 187–197
band around 3300 cm−1 due to the N–H stretching for
the ligand (L1)–(L5) is shifted to higher frequency (ca.
3400 cm−1) and broadened [21] in the corresponding
complexes (Tb1)–(Tb5) and (Dy1)–(Dy5), respec-
tively. The ligands containing NCH3 group (L6)–(L10)
exhibit peaks in the region 3000–2800 cm−1 due to
C–H stretching vibrations of NCH3 group along with
the Bohlmann bands. These peaks are missing in the
spectra of the corresponding complexes (Tb6)–(Tb10)
and (Dy6)–(Dy10). The C–H stretching absorptions
may be shifted to higher frequency and merged with
the broad peak [22]. The Bohlmann bands [23] which
occur in the region 3000–2750 cm−1 in the IR spectra
of the ligands are found to be missing in the spectra
of the corresponding complexes. The absence of these
bands reveals that there may be a conformational
change of piperidinone ring due to its complexation
with the metal ion through the lone pair of electrons
of the ring nitrogen. All the above observations lead
to the conclusion that the ring nitrogen is coordinated
to TbIII and DyIII ions with a slight conformational
change.
Table 7
Thermal analysis of the TbIII nitrate complexesa
Complex
Number
DTA peak
temperature (◦C)
Thermogravimetry
Decomposition product
Formula
Temperature
range (◦C)
Weight loss
found
(calculated) %
(Tb2)
[Tb(C18H19NO)(NO3)2(H2O)2]NO3
173+
228−
374−
484−
529−
185+
230−
410+
525−
174+
230−
237−
393−
423−
511−
202+
218−
367−
511−
174+
223−
365−
415−
520−
179+
235−
365−
437−
527−
193+
245−
390−
420−
170–190
200–490
5.76 (5.58)
[Tb(C18H19NO)(NO3)2]NO3
Tb(NO3)3
45.75 (46.62)
490–575
175–200
210–450
71.75 (71.07)
5.50 (5.46)
48.00 (47.75)
Tb4O7
(Tb3)
(Tb4)
[Tb(C19H21NO)(NO3)2(H2O)2]NO3
[Tb(C20H23NO)(NO3)2(H2O)2]NO3
[Tb(C19H21NO)(NO3)2]NO3
Tb(NO3)3
460–575
170–210
72.00 (71.68)
5.00 (5.31)
Tb4O7
[Tb(C20H23NO)(NO3)2]NO3
220–450
49.00 (48.84)
Tb(NO3)3
450–550
190–210
210–400
72.00 (72.27)
5.00 (5.46)
47.00 (47.75)
Tb4O7
(Tb5)
(Tb6)
[Tb(C19H21NO)(NO3)2(H2O)2]NO3
[Tb(C18H19NO)(NO3)2(H2O)2]NO3
[Tb(C19H21NO)(NO3)2]NO3
Tb(NO3)3
450–525
170–200
72.00 (71.68)
6.00 (5.58)
Tb4O7
[Tb(C18H19NO)(NO3)2]NO3
210–450
46.50 (46.62)
Tb(NO3)3
475–575
180–205
71.00(71.07)
5.00 (5.46)
Tb4O7
(Tb7)
(Tb8)
[Tb(C19H21NO)(NO3)2(H2O)2]NO3
[Tb(C20H23NO)(NO3)2(H2O)2]NO3
[Tb(C19H21NO)(NO3)2]NO3
210–450
47.50 (47.75)
Tb(NO3)3
475–575
185–210
72.00 (71.68)
5.00 (5.35)
Tb4O7
[Tb(C20H23NO)(NO3)2]NO3
225–450
49.00 (48.84)
Tb(NO3)3
a Here, (+) endothermic; (−) exothermic.

K. Selvaraj, C. Theivarasu / Thermochimica Acta 401 (2003) 187–197
193
The carbonyl stretching frequency of the ligands lie
around 1700 cm−1. This absorption is shifted to higher
frequency in the corresponding complexes. The higher
frequency shift may be due to conformational changes
that occur as a result of coordination of the ring nitro-
gen and not due to carbonyl group participation [5].
The presence of water molecules in the com-
plexes is shown by a broad absorption band in the
3600–3200 cm−1 region (merged with the NH ab-
sorption) due to O–H stretching vibration and a sharp
medium peak at 1624 cm−1 due to H–O–H bending
vibration [24].
The ionic nitrate group which has D3h symmetry,
has four fundamental vibrations, three of which are
IR active. Upon coordination as either a monoden-
tate or a bidentate ligand, the symmetry becomes C2v,
which has six infrared active normal modes of vi-
brations. The characteristic frequencies of coordinat-
ing nitrate groups ν1 to ν6 of the complexes are in
range 1290–1330, 1029–1040, 745–758, 1458–1480,
698–700 and 822–826 cm−1, respectively. The mag-
nitudes of ν4 − ν1 and ν3 − ν5 for TbIII complexes
are in the range 141–168 and 47–56 cm−1, respec-
tively, and for DyIII complexes 151–182, 48–58 cm−1
,
Table 8
Thermal analysis data of DyIII nitrate complexesa
Complex
Number
DTA peak
temperature (◦C)
Thermogravimetry
Decomposition product
Formula
Temperature
range (◦C)
Weight loss
found
(calculated) %
(Dy1)
(Dy2)
[Dy(C17H17NO)(NO3)2(H2O)2]NO3
172+
225−
375−
456−
550−
173+
213−
285−
407−
450−
517−
175+
248−
253−
374−
452−
515−
180+
215−
380−
465−
525−
202+
223−
370−
455−
528−
195+
245−
367−
465−
515−
170–200
220–475
5.50 (5.67)
[Dy(C17H17NO)(NO3)2]NO3
Dy(NO3)3
40.00 (39.51)
475–600
170–190
71.00 (70.66)
5.25 (5.55)
Dy2O3
[Dy(C18
H19NO)(NO3)2(H2O)2]NO3
[Dy(C18H19NO)(NO3)2]NO3
200–475
41.00 (40.81)
Dy(NO3)3
475–600
170–200
71.00 (71.29)
5.25 (5.43)
Dy2O3
(Dy3)
[Dy(C19H21NO)(NO3)2(H2O)2]NO3
[Dy(C19H21NO)(NO3)2]NO3
340–460
42.00 (42.06)
Dy(NO3)3
460–525
175–200
72.00 (71.90)
5.20 (5.32)
Dy2O3
(Dy4)
(Dy5)
(Dy9)
[Dy(C20H23NO)(NO3)2(H2O)2]NO3
[Dy(C19H21NO)(NO3)2(H2O)2]NO3
[Dy(C21H25NO)(NO3)2(H2O)2]NO3
[Dy(C20H23NO)(NO3)2]NO3
200–500
43.50 (43.26)
Dy(NO3)3
500–600
190–210
73.00 (72.48)
5.50 (5.43)
Dy2O3
[Dy(C19H21NO)(NO3)2]NO3
220–475
42.00 (42.06)
Dy(NO3)3
475–600
190–200
71.50 (71.90)
5.00 (5.21)
Dy2O3
[Dy(C21H25NO)(NO3)2]NO3
210–490
500–575
44.00 (44.41)
73.00 (73.04)
Dy(NO3)3
Dy2O3
a Here, (+) endothermic; (−) exothermic.

194
K. Selvaraj, C. Theivarasu / Thermochimica Acta 401 (2003) 187–197
respectively, suggesting that the nitrate groups are co-
ordinated as bidentate ligands [24,25]. Another band
at ca. 1384 cm−1 due to the ionic nitrate is also present
in the spectra. This observation, coupled with elemen-
tal analyses and conductance data, reveals the pres-
ence of one ionic and two bidentate nitrate groups.
Two new bands observed in the region 550–543
and 420–415 cm−1 are attributed to M–N and M–O
bonding, respectively [26].
b1/2 calculated [28] for these complexes are presented
in Table 6. The values of β are found to be less than
unity and the positive values of the bonding parameter
b1/2 and Sinha’s parameter δ indicate convalency in
the metal–ligand bonding [29]. The δ values are <1.0
in all of these complexes indicating weak covalent
character in the metal–ligand bond. The compara-
tively small magnitude of b1/2 values shows the par-
ticipation of the 4f-orbitals in the metal–ligand bond
to a very small extent [19]. The visible electronic
spectra of terbium(III) complexes show no significant
absorption.
3.3. Electronic spectra
The electronic spectra of dysprosium(III) com-
plexes have been recorded in methanol as solvent
and are found to be similar. In the UV region, a
strong band around 220 nm and a weak band around
260 nm are present which are attributed to π → π∗
and n → π∗ transitions, respectively, of the carbonyl
group of the ligand.
The absorption bands observed in the visible region
are due to f–f transitions. The tentative assignments
of bands for the dysprosium(III) complexes (Dy2) and
(Dy5) are given in Table 5. The spectra of the com-
plexes show a shift of bands towards lower energy,
compared with those of the aquo ions owing to the
nephelauxetic effect [27]. The nephelauxetic ratio β,
percentage convalency δ and the bonding parameter
3.4. Thermal studies
The simultaneous TG–DTA measurements of ter-
bium(III) and dysprosium(III) complexes were carried
out in air and their thermal data are given in Tables 7
and 8, respectively. The thermal studies have also
been carried out for the ligand (L5) and the thermo-
gram is shown in Fig. 1. The thermal curves of a few
complexes are given (Figs. 2 and 3). The TG–DTA
curves of terbium(III) and dysprosium(III) complexes
are similar. Generally, the thermal decomposition
takes place in three stages. The thermal curves of
all the complexes show an endothermic peak in the
170–210 ◦C temperature range. The mass loss at this
Fig. 1. TG–DTA of the ligand (L5).

K. Selvaraj, C. Theivarasu / Thermochimica Acta 401 (2003) 187–197
195
Fig. 2. TG–DTA of the complex (Tb5).
temperature corresponds to the dehydration of two
water molecules. The loss of water molecules in this
temperature range also indicate that they are coordi-
nated with the metal ion [30]. This is followed by the
decomposition of organic ligand in the temperature
range 200–450 ◦C (shown by an exothermic peak)
leading to the formation of lanthanide(III) nitrate.
The second stage of decomposition is supported by
the observation list the free ligand also undergoes
decomposition the same temperature range (Fig. 1).
The final residue corresponds to Tb4O7 and Dy2O3
for TbIII and DyIII complexes [31], respectively.The
thermal decomposition sequences of terbium(III) and
dyprosium(III) complexes are given in the following
Fig. 3. TG–DTA of the complex (Dy5).

196
K. Selvaraj, C. Theivarasu / Thermochimica Acta 401 (2003) 187–197
equations.
Acknowledgements
[Tb(L)(NO3)2(H2O)]NO3
We thank Dr. B. Sampath Kumar, Principal and
◦
170–210 C[Tb(L)(NO3)2]NO3
Secretary PSG College of Arts and Science for pro-
viding laboratory facilities. We also thank Tamilnadu
State Government, for the award of scholarship to C.
Theivarasu.
→
−2H2O
◦
◦
→
200–450 CTb(NO3)3
→
475–575 CTb4O7
−L
References
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where Ln: Tb and Dy.

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